The typical prior art exhaust muffler comprises a plurality of discrete tubes supported in parallel relationship to one another by a plurality of transversely extending baffles. The baffles generally will be of identical circular or oval peripheral configuration and will be aligned generally in register with one another. Some tubes in the array typically are perforated or louvered at selected locations along their length. Additionally, some tubes may extend greater distances than other tubes in the array. This typical prior art muffler further includes an outer shell that is wrapped around the transverse baffles such that the outer shell and adjacent baffles define chambers through which the tubes extend. The opposed ends of the muffler are closed by end caps or headers that are connected to the opposed ends of the tubular outer shell. The headers include at least one inlet and at least one outlet to provide communication with the chambers and tubes of the muffler. Inlet and outlet nipples or inlet and outlet tubes will extend through the inlet and outlet apertures of the headers to enable exhaust gas to flow into and out of the prior art muffler. Many prior art mufflers further include a separate outer wrapper which closely engages the outer shell for minimizing vibrations of the outer shell and the shell ring noise associated with such vibrations.
The above described prior art muffler generally is acceptable in attenuating the noise associated with the flow of exhaust gas from an engine. However, these prior art mufflers require a large number of separate components that must be manufactured and assembled in labor intensive manufacturing processes. The relatively large number of components may also result in an undesirable heavy muffler.
The conventional prior art muffler described above offers many internal design options but very few external design options. In particular, conventional prior art mufflers generally are limited to a rectangular plan view configuration, with the inlet and outlet extending from the opposed longitudinal ends. Unfortunately, the available space envelope on the underside of the vehicle often is not well suited to the rectangular shape required for the prior art conventional muffler. Thus, portions of the limited available space on the underside of the vehicle may not be properly utilized by the prior art muffler. This additional space often would help the exhaust system engineer to achieve the specified levels of noise and back pressure. Furthermore, the need to put inlet and outlet pipes at the opposed longitudinal ends of this prior art muffler often requires circuitous routing of the exhaust pipe and tail pipe with correspondingly great material costs.
Mufflers which comprise stamp formed components have been available for many years. Mufflers formed at least in part from stamped components offer the potential for reducing the number of components in the muffler. As a result, mufflers formed with stamped components can offer significant manufacturing efficiencies, at least partly in view of the potential for more automated manufacturing steps, as compared to conventional prior art mufflers.
The typical prior art stamp formed muffler has consisted of a pair of internal plates with opposed symmetrical registered channels defining an array of tubes, with portions of the tubes being perforated. The internal plates of the typical prior art stamp formed muffler are surrounded by a stamp formed external shell which defines a single large expansion chmber surrounding the perforated tubes. Prior art mufflers of this type generally are not able to satisfy the noise attenuation requirements for vehicles in the United States. More particularly, these prior art stamp formed mufflers often will be unable to adequately attenuate at least one narrow range of low frequency noise. Examples of prior art stamp formed mufflers of this general type are shown in British Patent No. 632,013 which issued to White in 1949; British Patent No. 1,012,463 which issued to Woolgar on Dec. 8, 1965; Japanese Published Patent Application No. 59-43456 which was published in 1984; and, U.S. Pat. No. 4,132,286 which issued to Hasui et al. on Jan. 2, 1979.
A slight variation of the above described typical prior art mufflers is shown in U.S. Pat. No. 4,415,059 which issued to Hayashi on Nov. 15, 1983 and shows a stamp formed straight-through muffler with two short punch formed tuning tubes extending transverse to the through tube. The muffler shown in U.S. Pat. No. 4,415,059 would not adequately attenuate all ranges of noise, such as low frequency noise.
Other prior art stamp formed mufflers have merely included a circuitous array of tubes and chambers. Noise attenuation in mufflers of this type presumably is achieved by the periodic expansion of the exhaust gases flowing from one of the tubular sections into one of the larger chambers. These mufflers also are functionally quite limited. Examples of mufflers of this type are shown in U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972 and U.S. Pat. No. 3,176,791 which issued to Betts et al. on Apr. 6, 1965.
Still other prior art stamp formed mufflers include conventional tubular components disposed within a stamp formed outer shell. These prior art mufflers include UK Patent Application No. 21 120 318 and U.S. Pat. No. 4,109,751 which issued Kabele on Aug. 29, 1978.
Recently there have been several significant advances in stamp formed mufflers, as disclosed in patents and pending applications which are assigned to the assignee of the subject application. In particular, extremely effective and efficient mufflers are shown in U.S. Pat. No. 4,700,806 which issued on Oct. 20, 1987 to Jon Harwood and in U.S. Pat. No. 4,736,817 which issued from a continuation of the application leading to U.S. Pat. No. 4,700,806. These two patents show mufflers formed from a pair of plates that are formed to define an array of registered channels, with opposed channels defining an array of tubes. At least one of the tubes in the array defines a tuning tube having a length which extends along the abutting surfaces of the plates from which the tubes are formed. In this manner, the length and cross section of the tuning tube can be carefully selected in accordance with the frequency of the sound to be attenuated. The mufflers disclosed in U.S. Pat. Nos. 4,700,806 and 4,736,817 further include an external shell mounted to the plates and formed to define at least an expansion chamber and a low frequency resonating chamber which are separated from one another by a baffle crease. The low frequency resonating chamber is disposed to communicate with a corresponding tuning tube. The volume of the low frequency resonating chamber and the length and cross-sectional dimension of the tuning tube can be selected to properly attenuate one or more specific narrow ranges of low frequency noise that are not properly attenuated by the expansion chamber. Efficient methods and apparatus for manufacturing mufflers in accordance with U.S. Pat. Nos. 4,700,806 and 4,736,817 are shown in U.S. Pat. No. 4,847,865 which issued on July 18, 1989 and U.S. Pat. No. 4,860,853 which issued on Aug. 29, 1989. The two preceding patents also are assigned to the assignee of the subject invention.
Several of the mufflers shown in the above referenced patents owned by the assignee of the subject invention show a plurality of tubes passing through the baffle crease which separates the chambers of the muffler. This construction has led to the creation of pockets between the tubes passing through the baffle creases. The existence of these pockets does not appear to affect the life of the mufflers. However, it has been suggested that the pockets can accumulate foreign materials which conceivably could affect the metal in the vicinity of the pockets. U.S. Pat. No. 4,865,154 issued to Hanson et al. on Sept. 12, 1989 and attempts to address the undesirable accumulation of foreign material in the vicinity of pockets in the baffle crease of the muffler. More particularly, U.S. Pat. No. 4,865,154 provides holes passing vertically entirely through the pockets to enable drainage of foreign material that might otherwise accumulate in the pockets. It is believed, however, that any material that might accumulate in the pockets of the baffle crease would be in the nature of a thick sludge that would clog the drainage hole suggested by U.S. Pat. No. 4,865,154.
Several patents and pending applications that are assigned to the assignee of the subject invention provide more desirable options for eliminating pockets in the baffle crease of the muffler. For example, U.S. Pat. No. 4,836,330 which issued on June 6, 1989 shows a plural chamber muffler with only a single tube extending through the baffle crease. The provision of only one tube extending across the baffle crease avoids the creation of the potentially objectionable pockets. U.S. Pat. No. 4,860,853 issued on Aug. 29, 1989 to Walter G. Moring, III and shows mufflers where the tubes are defined between an internal plate and an external shell. Thus, the external shell does not have to deform down to meet the internal plate, and external pockets can be avoided. Still another muffler which avoids external pockets is shown in pending application Ser. No. 471,288 which was filed by VanBlaircum et al. on Jan. 26, 1990 and shows a muffler having at least one transverse tube which is disposed in register with the baffle crease. Thus, the baffle crease is of uniform depth and pockets can be avoided entirely. The disclosures of the above identified patents and pending applications that are assigned to the assignee of the subject invention ar incorporated herein by reference.
Although the above described prior art stamp formed mufflers that are assigned to the assignee of the subject invention offer many desirable features, there are some instances where the tuning requirements of the vehicle require a muffler with at least one baffle crease and with a plurality of tubes extending across the baffle crease. For these instances, it is desirable to provide a muffler that avoids the creation of pockets that conceivably could accumulate foreign materials.
In view of the above, it is an object of the subject invention to provide a stamp formed muffler that is substantially free of external pockets that could accumulate foreign materials.
Another object of the subject invention is to provide a stamp formed muffler having a plurality of chambers separated by a baffle crease, but with no pockets formed in the upwardly facing portion of the baffle crease.
An additional object of the subject invention is to provide a stamp formed muffler having a plurality of tubes extending across a baffle crease but without pockets defined in the upwardly facing portion of the baffle crease.
Still a further object of the subject invention is to provide a stamp formed muffler having a baffle crease separating two chambers and with only downwardly facing pockets defined in the baffle crease.